Recently, many copying machines are combined with sheet post-processing apparatuses with post-processing functions such as binding or punching sheets having images copied thereon in order to automate the process.
For the conventional sheet post-processing apparatuses, for example, European Patent No. 346,851 discloses a sheet post-processing apparatus wherein an endless transport belt is driven in one direction, and stapled sheets are discharged from a processing tray onto a stacking tray by a push-out member provided on the transport belt. In the above apparatus, the stacking tray can be raised and lowered so that the top surface of the sheets stacked on the stacking tray is set at virtually the same height as the processing tray.
Another conventional sheet post-processing apparatus is known as disclosed in European Patent No. 371,403 wherein a stacking tray can be moved vertically and horizontally, sheets are placed over the stacking tray and the processing tray, and after a cycle of copying process is completed, a set of sheets is stapled and discharged onto the stacking tray using a discharge roller and swinging roller or using an ejector. In the non-processing mode, the swinging roller is brought in contact with the discharge roller, and sheets fed from the copying machine main body are discharged onto the stacking tray, while in the processing mode, the swinging roller is kept apart from the discharge roller, and sheets fed from the copying machine main body are temporarily stored on the processing tray, thereafter, the swinging roller is brought in contact with the discharge roller so as to discharge the sheets onto the stacking tray.
U.S. Pat. No. 5,137,265 discloses a sheet post-processing apparatus wherein a recessed portion on the stacking tray corresponds to a needle for fastening the sheets in the processing mode, The above apparatus is also arranged such that in the processing mode, when transporting sheets which are larger than a predetermined size, the sheets placed over the processing tray and the stacking tray are discharged onto the stacking tray by the discharge roller and the swinging roller, while when transporting sheets which are smaller than a predetermined size, sheets remain placed over the post-processing tray and the stacking tray without being discharged. Additionally, in the processing mode, an auxiliary tray is moved to place the stacking tray on an extended line of the processing tray so as to discharge a processed set of sheets onto the stacking tray from the processing tray.
A still another conventional sheet post-processing apparatus is disclosed in Japanese Laid Open Patent Application No. 147815/1993 (Tokukaihei 5-147815) wherein among copy sheets conveyed from the main body of the copying machine, sheets not to be processed are directly discharged onto a stacking tray, while sheets to be processed are supported on the processing tray, and after being processed, a processed set of sheets is discharged onto the stacking tray by the pushing member. The above described sheet post-processing apparatus will be explained below with reference to simplified structure shown in FIG. 32 and FIG. 33.
In the non-processing mode, in which sheets are not processed, a sheet P discharged from a copying machine main body (not shown) is transported into the apparatus through sheet guides 101 and 102 as shown in FIG. 32. Then, the sheet P is further transported to a discharge roller 106 by transport rollers 103 and 104. Thereafter, the sheet P passes between the discharge roller 106 and a pressure roller 105 to be pressed onto the discharge roller 106, thereby discharging the sheet P onto a stacking tray 107 by a transporting force.
On the other hand, in the processing mode in which, for example, sheets are stapled, as shown in FIG. 33, the pressure roller 105 is moved upward together with a sheet guide 108, and an opening of a discharge section 109 is formed between the pressure roller 105 and the discharge roller 106. In this state, the sheet P transported by the transport rollers 103 and 104 is dropped onto a slanted processing tray 110 when it becomes apart from the transport rollers 103 and 104. The movement of the sheet P is supported by a rotary vane 112 made of a rubber being rotated in a direction of A until the sheet P reaches a member 111 for stopping the trailing edge of the sheets P. Then, the sheets P are aligned in a widthwise direction by an aligner plate 113 which is driven in a widthwise direction. When a predetermined number of sheets P are placed on the processing tray 110 after repeating the above process, a stapling process is carried out on the sheets placed on the processing tray 110 by the stapler 114. Thereafter, with the movement of the sheet push-out member 115 in a direction of C, the sheets P on the processing tray 110 are discharged onto the stacking tray 107 through the discharge section 109.
In the above conventional sheet post-processing apparatus, however, the pressure roller 105, which transports the sheet P together with the discharge roller 106, presses the discharge roller 106 in the non-processing mode, while in the processing mode, the pressure roller 105 becomes apart from the discharge roller 106. Namely, the contacting state between the pressure roller 105 and the discharge roller 106 and a distance between the discharge roller 106 and the pressure roller 105 change between the non-processing mode and the processing mode. Thus, the pressure roller 105 cannot be pressed onto the discharge roller 106 in a stable condition, thereby presenting the problem that a sheet may be stuck or slanted when being discharged in the non-processing mode.